The present invention relates to a hydraulic shock-absorber having a rod guide for guiding a piston rod sliding in a cylinder which rod guide is provided at one end of the cylinder and which rod guide butts, at an extension stroke end of the piston rod, against a rebound stopper secured to the piston rod.
In a conventional hydraulic shock-absorber used in an automobile etc., there is known a rod guide made of sintered metal as one against which a rebound stopper secured onto a piston rod butts. However, regarding a rod guide made of a sintered metal, there is a problem in view of the increased weight thereof and the increased cost of the production thereof. In recent years, there is such a tendency as a rod guide 8 shown in FIG. 4 which is made by press-working a plate material has been used. However, in a case of the rod guide manufactured by press-working the plate material, there is a problem regarding the strength thereof. Namely, as shown in FIG. 4, when a rod guide 8 butts against a rebound stopper 4, concentrated force is caused in an arrow direction with the result that the rod guide is deformed as shown in FIG. 5, that is, an inner cylindrical portion 8b of the rod guide is deformed-and-displaced upward. As the result thereof, the sliding resistance of the piston rod 5 increases, causing a problem that it cannot slide smoothly. As a rod guide capable of preventing this deformation, there is one in which a bent portion is formed in a part of the butting portion of the rod guide against which portion the rebound stopper butts, as shown, for example, in JP-A-10-281204, or there is another in which a separate member is attached onto the butting portion of the rod guide as shown in JP-Z-2520280, whereby in each of these conventional rod guides the strength against shock is enhanced to thereby prevent the rod guide from being deformed.
The inventors of the invention have found that, in the above case where the bent portion is formed in a part of butting portion of the rod guide against which part the rebound stopper butts, the rebound stopper does not butt against the part where the bent portion is formed, so that only such a portion of the rebound stopper as to butt against the rod guide comes to be worn locally, thus resulting in a problem of poor durability regarding the rebound stopper. In another case where the separate member is attached to the butting portion of the rod guide against which portion the rebound stopper butts, the number of shock-absorber parts come to increase, resulting in a problem of increased manufacturing costs.
In view of the above, it is an object of the invention to provide a hydraulic shock-absorber in which a force applied to a rod guide by a rebound stopper is dispersed so that the rod guide may not be deformed.
According to the first aspect of the invention capable of realizing the object, there is provided a hydraulic shock-absorber comprising: a cylinder provided with ends; a piston rod sliding in the cylinder; a rod guide for guiding the piston rod sliding in the cylinder which rod guide is located at one of the ends of the cylinder; and a rebound stopper secured to the piston rod which rebound stopper butts against the rod guide at an end of extension-stroke of the piston rod, the rod guide being made of a plate and comprising:
an inner cylindrical portion corresponding to an outer periphery of the piston rod;
a butting planar portion against which the rebound stopper butts and which planar portion is extended radially of the cylinder from a lower end of the inner cylindrical portion;
a butting slant portion against which an outer peripheral portion of the rebound stopper butts and which slant portion is extended downward obliquely from an outer end of the butting planar portion toward an inner periphery of the cylinder; and
a cylindrical fitting portion fitted onto the inner periphery of the cylinder which portion is extended upward from a lower end of the butting slant portion. Because of this structure, force applied by the rebound stopper to the rod guide is not concentrated in one direction with the result that the rod guide is prevented from being deformed, whereby the piston rod can always slide smoothly. In the specification, the terms xe2x80x9cupwardxe2x80x9d and xe2x80x9cupperxe2x80x9d are defined to mean a direction in which the piston rod advances during the extension stroke thereof and a location or level which is spaced in this direction (, that is, in the axial direction of the shock-absorber) more apart from the piston end located within the cylinder than that of another compared therewith, respectively, and the terms xe2x80x9cdownwardxe2x80x9d and xe2x80x9clowerxe2x80x9d are defined to mean another direction reverse to the xe2x80x9cupwardxe2x80x9d direction and another location or level which is nearer from this piston end than that of one compared therewith. Further, the term xe2x80x9caxialxe2x80x9d or xe2x80x9caxiallyxe2x80x9d is defined to mean a direction of the axis of the cylinder which axis is identical with the axis of the shock absorber of the invention.
According to the second aspect of the invention, the butting slant portion may be formed to have a straight, axially sectional shape when viewing the axial section of this slant portion. In this structure, the butting slant portion can be formed easily at a step of manufacturing the rod guide, thus lowering the costs of manufacturing the rod guide.
According to the third aspect of the invention, the butting slant portion may be formed to have a curved, axially sectional shape when viewing the axial section of this slant portion. In this structure, it becomes possible to disperse force, which is applied by the rebound stopper to the rod guide, in directions of an angularly wider range than that of the slant of the straight section to thereby prevent more surely the rod guide from being deformed, thus allowing the piston rod to always slide smoothly.